Flashbacks - has anyone got experience of them?

Flashbacks can be a symptom of PTSD but true flashbacks happen while awake and they go on for months after the event that triggered them. I think what you are experiencing sounds like a normal reaction to a really diificult situation which should resolve in the next few days or may take a little longer.
I think that while being reassured that there was nothing you could do you might feel better if you do do something.
Was this one student who did 2 dangerous things or incidents involving 2 different students?
If it was the former I would be trying to get some additional support or this student and trying to find out what was going on with them
If it was the latter you probably need to do afull risk assessment of the classroom, materials and equipment being used etc .
This should help you be clear in your own mind that everything you could do to keep students safe has been done.

It was early in the final term in September, not long after our 'summer break', when we decided to play some pool and sink a few beers at the local power station club. At some point along the line, it was suggested that we stay with some fellow Cuban teachers near the town. I was especially keen on that suggestion as my elderly housemate was slightly the worse for wear by then, and he often struggled with the dirt roads between that town and our rural school.
To cut a long story short, we decided in the end to head back at dusk. I was a bit apprehensive so I asked the youngest amongst us, an eagle eyed Cuban, to sit in the cab with the driver to keep him on task. I sat in the back of the pickup with the other Cuban. What gets me about what happened next is not that the accident happened but that it bears out the old saw that life doesn't imitate art, it apes bad television.
My last words to my good friend as the car began to slide were: whatever you do, don't let go of the box of wine. He banged his head and was tossed clear of the vehicle and he then hit his head on a rock. He survived that as we got him to a clinic, Eventually, they took him to Angola and from there to Cuba- where he died from a secondary infection. Suffice is to say that I don't go too long without thinking about him, and I always think of that when some jackass or other says that they have no regrets in life. If you have no regrets then you were either very lucky or you are simply pig stupid!

Nightmares are just your brain's way of dealing with and processing the stress caused by the event. As it is only a couple of weeks then it is very likely that these will subside pretty quickly.
Flashbacks tend to happen whilst awake and are triggered by the smallest sights, sounds or smells. It is a bit like being flashed back into the event as it happened, in my case it was usually only for a couple of seconds or so as I managed to shut it down over the years, but in the time it happened then it seemed very real and I lost what was really going on around me. It did get less over the years but came back with avengeance last year after a couple of years of a lot of different stresses and I eventually got treatment for PTSD.
What you are describing is frightening but different. Give it some time and you should feel better, if not ask to speak to someone in a counselling role at school. Don't go to your doctor unless you get severe symptoms for months, they tend to medicate you with ADs which can make symptoms a lot worse. Just remember that although the events could have been fatal, they weren't. Have a relaxing weekend and have some rest, do something for yourself like have a long soak in the tub with lots of bubbles, a bottle of wine and your favourite music and just take care xx

What you describe is an absolutely normal reaction to a traumatic incident. Violent nightmares are one of the characteristics of post tramatic stress disorder (although you do not have to be suffering from full-blown PTSD to have them).
It happens when the memory of a traumatic incident is stored in the part of the brain called the amygdala, which deals with emotion, rather than the hippocampus, where past experiences are stored as factual narrative. At the moment, your memory of the incident triggers the emotional fear you experienced at the time and that part of your brain is hyper-active in sleep.
How to stop it? I was taught to write out the experience over and over again. This is more effective than retelling orally as you include more detail and order the memory more effectively. The act of doing this helps the memory to be transferred from the amygdala to the hippocampus.
The above is a cognitive behaviour therapy technique. If you want to access other CBT techniques that might be helpful, a great self-help website is Moodgym http://moodgym.anu.edu.au/welcome
Ignore the bit where it says it offers CBT techniques to help combat depression - it also works well for post trauma stress.
Post trauma nightmares are horrible and distressing. They do leave you feeling exhausted and washed out and, yes, have bad headaches. The more you can work through the memory, the quicker it will stop troubling you. If you find the nightmares won't go, go to see your doctor as you may need some treatment.
Cor, I used to pay &pound;100 per hour for what I've just passed on to you!!

Thank you for your kind replies.
The fact that I am mostly having problems at night is I think reassuring. I do find the events keep coming back into my head at random through the day but I think that is probably down to the continuous waking at night with them rather than being full-blown flashbacks.
The incidents were with two different students - who by complete and random chance managed to do nearly exactly the same as each other. I could describe both of them with a choice selection of expletives here but will resist from doing so.
Gardening Leaves - interesting what you say about writing things out helping. I have not done so up until now as I feared it might make me dwell on it more - might give it a go now and see what happens. I too am a veteran of the CBT world and in the daylight hours can halt my thoughts when they go into the negative pattern - it is just at night that they are refusing to behave!
The problem may be solved tonight though as can't see me having time to go to sleep with the size of my marking pile so that should get rid of the nightmares!

I too have had PTSD due to a traumatic event. I would say as long as the intrusive thoughts are in your head replayed during sleep that this will fade. If this becomes a problem while you are awake then you need to seek some help.

I was seen by a trainee clinical psychologist today who was, not surprisingly, more interested in taking her forms for a spin than doing something to help me. I particularly objected to her contesting that I get the shakes, simply because I am not on a par with someone with Parkinsons. I was also struck by her obsession about what exactly I wanted to happen next, as if simply by clicking my heels three times I can break the habit of a life time. Incidentally, teaching- unlike counselling- forces its managers to never admit weakness, and the results are pretty predictable as a consequence.
I was denied a course of CBT or Psychotherapy on a techincality, even though I have a nasty tendency to scream that I am dying, amongst other things. I'm no expert but that may well be PTSD, writ large.

Roboteer-Are the incidents in any way related to what you originally had the CBT for? It could be that it is triggering off something deeper.
Pangar-Maybe you could start your own thread about your concerns? The psychologist is asking you what you want to happen next as the point of the therapy is to work together to solve your concerns. They don't tell you what to do and you will be disappointed with therapy if you expect them to be in control. Change is hard work and they will support you through it if you let them.

Pangar, I couldn't even get to see a psychologist on the NHS, the doctor would only recommend tablets as our mental health services in the area have a 6 month waiting list.
I eventually went to a clinical hypnotherapist which I found helped enormously. It cost me a lot but I got my sleep and sanity back. I had tried a couple of different counsellors and gone through a course of EMDR, none of which had helped much, mainly because the psychological and physical symptoms had become detached as I had spent an awful lot of energy supressing the symptoms over the years.

Unlike the black spot behind you, your response has been very useful. I had to wait for months for a referral to a clinical psychologist, as you say. I am literally sick and tired of taking so many tablets, none of which seems to do the trick. I did dally with getting a full MOT from a private doctor but the cost involved is not to be sneered at, unless of course you've tapped into a rich black spot that is.

I was told today that I can't get a CBT or Psychotherapy referral as I had previously insisted that the local MH team answer the question which my Sleep Study Centre disowned all responsibility for: what precisely is the cost:benefit analysis in prescribing me with heavy duty tranquilisers which don't work for more than a few hours but cause severe side effects? This has not stopped the trainee clinical psychologist from passing the detailed transript of our hour and a half consultation over to the MH team without bothering to give me a copy. Frankly, I find it all patronising, infantilizing and infuriating.
Can I just say yet again that this so-called 'caring profession' does its professionals a severe disservice by denying them the equivalent of supervision, where they can share their doubts and concerns in a supportive environment. The consequences of the macho management ethos leaking downwards like a clapped out battery are there for all to see, and they are just as messy!